While Blizzard did not announce when they will release the new portraits, it seems that they’re already in the game as a part of this patch. You unlock them just like your Golden portraits – by hitting X wins with a given class. It was 500 for the Golden Portraits, and it’s 1000 for this new batch. Keep in mind that only ranked and Arena wins count for the portraits – any Casual, Brawl or PvE wins do not.
Here’s how all of the new portraits look like: